1. Field of the Invention
The invention relates to a continuous process for shaping, polymerizing, and optionally drying porous polymeric foam from water-in-oil high internal phase emulsions (HIPEs).
2. Description of the Prior Art
Water-in-oil emulsions are dispersions of discontinuous or discrete water particles commonly referred to as the "internal" aqueous phase in a continuous or "external" oil phase. Emulsions can contain as much and more than 70 volume percent internal phase. These are often referred to as high internal phase emulsions. The volume fraction of the internal aqueous phase in such emulsions can be as high as 90 percent and frequently is as high as 95 percent with some HIPEs being reported as high as 98 percent aqueous phase.
The use of high internal phase emulsions (HIPEs) in forming porous polymeric materials is well known and is described, for example, in Shell Oil Company (Shell) U.S. Pat. Nos. 5,210,104 and 5,200,433; Lever Brothers Company (Lever) U.S. Pat. Nos. 4,536,521 and 4,788,225; and The Procter & Gamble Company (P&G) U.S. Pat. Nos. 5,147,345; 5,331,015; 5,260,345; 5,268,224 and 5,318,554. In the described HIPEs, the external oil phase typically comprises a vinyl polymerizable monomer, such as 2-ethylhexyl acrylate and styrene, and a cross-linking monomer such as divinylbenzene. The internal aqueous phase typically comprises water, a radical initiator (if one is not already present in the oil phase) and an electrolyte. To form a stable emulsion, a surfactant is added to the oil phase prior to emulsification. Commonly used emulsion stabilizing surfactants include, for example, nonionic surfactants, such as sorbitan esters (e.g., sorbitan monooleate and sorbitan monolaurate). The resulting emulsion is then subjected to polymerization conditions which are sufficient to polymerize the monomers in the oil phase to form a porous polymer.
Ideally, one would like to produce polymerized HIPE foam in a continuous manner, thereby making efficient use of equipment space and volume while simplifying the production process. Continuous processes for the production of HIPE have been documented (see for example U.S. Pat. Nos. 3,565,817; 3,946,994; 4,018,426; 4,844,620; 5,149,720; 5,198,472; 5,250,576; and 5,827,909) however all of these patents fall short of a fully continuous process by not addressing how to continuously shape, polymerize, and dry the HIPE once prepared.
U.S. Pat. Nos. 3,565,817; 3,946,994; 4,018,426; and 4,844,620 disclose continuous processes for the production of high internal phase emulsions (HIPEs) but do not address shaping, polymerizing or drying the emulsion.
U.S. Pat. Nos. 5,149,720; 5,198,472; and 5,250,576, issued to Des Marais et al., as well as U.S. Pat. No. 5,827,909, issued to Des Marais disclose continuous processes for the production of polymerizable high internal phase emulsions (HIPEs). These patents teach that the HIPE, once prepared, can be polymerized by placing the HIPE emulsion in a suitable polymerization container and subjecting the emulsion therein to curing conditions. Therefore, the disclosed process, including HIPE preparation, shaping, polymerization, and drying is limited to a batch or semi-batch process.
A recent attempt to achieve a more complete continuous process is U.S. Pat. No. 5,670,101 ('101 patent), issued to Nazim et al., which discloses a process whereby a polymeric "tube" is filled with HIPE. The HIPE-filled tube is then spooled and polymerized. The primary disadvantage of the process disclosed in the '101 patent lies in the fact that it is actually a semi batch process rather than a continuous process. In the '101 process, tubes are filled with HIPE and then wrapped on a spool until the spool is full. The spool is then removed from the line for polymerization while another spool is wrapped. (see, for example, column 7 lines 39 ff.). The invention of U.S. Pat. No. 5,670,101 is more accurately described as a process of semi-continuously filling a plastic tube with a polymerizable HIPE. Further, the process of the '101 requires one to unwrap the polymerized foam from the spool, remove the bag from the HIPE and either discard the bag or re-implement at the beginning of the process.
Unfortunately, while the continuous production of HIPEs is known, current technology is limited to batch or semi-batch processes for shaping, polymerizing and drying the HIPE. It would be desirous to have a continuous process for shaping, polymerizing and drying polymerized HIPE foam so that the whole process of HIPE foam production could be continuous.
In contrast, the invention of the instant application is continuous in nature all the way through the drying of the final HIPE foam. Unlike prior art processes, the instant invention requires no interruption of the process from the making of the HIPE through the curing and drying process of the HIPE. The process of the instant invention overcomes the disadvantages of the prior art, since it does not require the HIPE to be placed in containers for polymerization and then removed again for drying and/or use; nor does the process of the instant invention require the HIPE to be place in bags which need to be wrapped, unwrapped and re-implemented or discarded. Rather, the invention of the application uses a continuous HIPE web to move the HIPE through the process.